Process of treating dry stereotype matrices



May 13, 1930- A. w. COCHRAN ET AL E758+243 PROCESS OF TREATING DRY STEREOTYPE MATRICE Filed Feb. 8, 1928 @www Patented May 13, 1930 UNITED STATES PATENT OFFICE ALBERT W. COCHRAN AND HENRY W. DEWEY, OF4 PORTLAND, OREGON PROCESS 0F TREATING DRY STEREOTYPE MATRICES Application led February 8, 1928.

Our invention relates to the art of making stereotype printing plates from so-called dry matrices. Unless these matrices are perfectly made poor castings will of course result.

At the present time, a great many newspapers are using these matrices, which are made of pulp such as is used in making newsprint. The texture of the dry matrix is much coarser than the Wet matrix. The imprint surface thereof, as disclosed by microscopic examination, has innumerable small cavities or pores, and much loose fiber. Hence, When making castings With one of these matrices, the metal tends to enter the said cavities or pores, and in consequence the stereotype plate Will not have'tliat smooth finish essential to making perfect imprints. Furthermore, the molten metal poured onto these matrices tends to become interlocked with the loose fibers thereof, Which results in the tearing of the impressed face of the Inatrix when the cooled stereotype plate is removed and renders the matrix unfit for further castings.

Fig. -1 shows a plan view of a section of a matrix in Which crevices were caused during the process of making the matrix; said crevices not being readily perceptible to the naked eye.

Fig. 2 illustrates diagrammatically, on a highly magnified scale, a section of a matrix with the metal cast therein for making the stereotype, and further illustrates that unless the upper layers or laminae of the paper mat are treated, as provided by our invention, minute portions of the metal cast in the matrix will enter said pores and interlock With the encompassing loose fibres of the matrix as indicated at a; and with the removal of the stereotype sections of the said surface will be torn away, as illustrated by Fig. 3 at b, resulting in the production of a defective stereotype, and a defective or poor print by the latter, as illustrated by Fig. 4 at c; which defect may be a white spot, or blur, or both, in a portion of the printed letter.

Figs. 5 and 6 further illustrate, diagrammatically, said cause and effect; Fig. 5 being a cross section on the line 5 5 of Fig. 1 of Serial No. 252,936.

both the matrix and stereotype case therein, and Fig. 6 being a similar cross section of the stereotype alone. Note the interlockin at d in Fig. 5, and the resulting imperfect etge of the printing surface occasioned at e in Fig. 6. And in Fig. 7 We have shown diagrammatically a small. highly magnified section of a matrix, the surface of Which has been coated as indicated by the heavy line fin conformity with our invention, thus producing a smooth surface filling the exposed pores and binding down any loose fibres of the matrix, and thus preventing any portions of the metal cast therein from entering and interlocking with said pores or said fibres.

The object of our invention is to provide a simple, efficient treatment for the face of these dry matrices, so that stereotype plates may be cast therein Without danger of any of said undesirable results occurring; and assuring the production of a perfect stereotype plate.

The said objectionable results, incidental to the use of dry mats, have heretofore been recognized, and attempts made to avoid them. To this end the general practice in the making of these matrices is to apply oil to the impressed surface thereof, for example a combination of kerosene and neats-foot oil just prior to the casting of the plate. Dry infusible powders, such as French chalk or graphite have also been used, With varying and unsatisfactory results.

The objection to such treatment is that unless the oil is vaporized or driven well into the matrix surface bv a number of preliminary roastings before a casting is made, the surplus oil, remaining on the face of the matrix will produce gas pockets in the hot metal, and cause White spots in the type faces and solid characters of the stereotype plate, spoiling the same.

Furthermore, matrices which have been treated with oil do not eiiciently resist the action of the molten stereotype metal and quickly deteriorate limiting the number of castings which may be made from the same matrix.

7e discovered that the undesirable effects were voidable by facing the surface of the mat in which the plate is cast with a dry powdered coating, formed of a fatty base which at normal temperatures is solid and may be reduced to an impalpable powder, and has the property of meltingat the temperature produced in the matrix scorcher, and will onl vaporize to a negligible degree under the eat of the molten stereotype metal, thus producing the required non-adherent property in said surface of the mat, also binding the loose fibers of the pulp compositionl in place.

We further discovered that zinc stearate is especially adapted for practicing our invention. This compound, of a fatty acid and a metallic salt, has the property of melting to its liquid form in the temperature produced in the matrix scorcher producing a thin liquid film, well adapted to spread itself over the face of the matrix, and to be quickly absorbed; in that way impregnating the matrix and filling the pores, and binding the loose fibers of the pulp down, and giving the face of the matrix a smooth, unbroken even surface capable of producing a clean perfect stereotype plate an avoiding the forming of any coating on the face of the matrix which might interfere with the making of a perfect castin An incidental result of our invention is to make the face of the matrix more resistant to the action of the molten stereotype metal so that the number of castings that may be made from a single matrix is materially increased.

Another incidental result of our invention, is it rovides a method for facing the matrix whic is easily, convenientl and expeditiously applied in practice. ur invention at most requires the matrix to be subjected to only one preliminary heating, while in the present practice consisting in the treatment of the matrix with oil as many as three preliminary roastings are frequently required, in order to assure that all the surplus oil has been driven from the face of the matrix, and thus prevent the tendency to form gas pockets from the vaporization of the oil due tothe heat of the molten stereotype metal.

These results both `on stereotype mats treated with our process and those which have not so been treated are hereinafter illustrated with reference to the accompanying drawings.

In these drawings:

Fig. 1 shows a plan view of a section of untreated matrix;

Fig. 2 shows a highly magnified section through the matrix;

Fig. 3 shows an imperfect matrix caused by the interlocking of the metal of the stereotype plate with the fibers of the matrix;

Fig. 4 shows the resulting imperfection in the printed letter caused by the imperfect stereotype formed from the matrix shown in Fig: 3;

ig. 5 shows a section taken on the line 5-5 of Fig. 1;

Fig. 6 shows a similar section taken through the stereotype plate alone, and

Fig. 7 is a broken highly ma ified section of the matrix coated in accor ance with the invention.

In act-ual practice we have obtained the best results, by taking the humidored matrix, after the t pe characters have been impressed on it, an first subjecting the matrix to a preliminary roasting, for approximately a minute to reduce the moisture content and make it more receptive to the application of the zinc stearate, which is spread evenly over its face, care bein taken to ll all the ty e` impressions in or er that the breaks in t e matrix at the bottom of the said impressions may be closed by the melting of the zinc stearate. Then the matrix is placed in the usual course of the process of drying and forming, in the matrix scorcher, where the zinc stearate, 'simultaneously with the drying and forming, melts and is absorbed and impregnates the face of the matrix, giving it a non-adherent surface.

The matrix is permitted to remain in the said scorcher for the proper length of time to roduce the required forming and drying an is then taken out, ready for the casting of the stereotype plate, without additional or lon er steps in the preparation of the matrix.

e have also found it most advantageous to add to the zinc stearate, a small proportion of powdered graphite in a mechanical mix-Y ture to eliminate the tendency of the melted zinc stearate of running together and collecting at one place on the face of the matrix, by ho ding the particles spread out over the face thereof to insure even, uniform absorption by the matrix.

Furthermore we have found by intermixing the powdered graphite with the zinc stearate in the presence of the gas arising from naphthalene crystals that the resulting intermixture tends to work more smoothly onto the matrix and to adhere more closely thereto before being melted.

Though we have described our process as adapted to be used just prior to the casting of the stereoty e plate, it may equally well be applied to t e matrices, as they are produced from the paper mill.

That is, the matrices may be treated with the zinc stearate, in the paper mill, and sold, toynewspapers and the like, who may then use them without further treatment in the regular course of casting stereotype plates.

Also the zinc stearate may be applied on the dry finished matrices or on the so-called conditioned matrices, which has been humidored in the mill and sold to the users, in an already moistened state.

We claim:

1. In the process of making stereotypes, the method of preparing the matrix which consists in coating the face thereof with, zinc s stearate, thereby to fill in the interstices of said face in the roasting of the matrix, and rendering the said face smooth, unbroken and non-adherent to the cast thereon.

2. In the process of making stereotypes, the

lo method of preparin the matrix which consists in coating the ace thereof with, a powdered substance solid under normal temperature and having a fatty base, intermixed with a relatively small proportion of powdered l graphite said intermixture characterized in that it has the roperty of melting at the temperature pro uced in the roasting of the matrix and vaporizes only to a negligible degrec underthe temperature of the metal cast 1n the matrix, thereby to fill the interstices of, and renderin the face of said matrix smooth, unbroken ang non-adherent to the cast thereon.

3. In the process of making stereotypes, the

method offpreparin the matrix which consists in coating the ace thereof with, a metallic salt of a fatty acid, intermixed with a relatively small proportion of powdered graphite said intermixture characterized in 3o that it has the roperty of melting at the temperature produced in the roasting of the matrix and vaporizes only to a negligible degree under the temperature of the metal cast in the matrix, thereby to fill the interstices of,

and renderin the faceof said matrix smooth,

unbroken an non-adherent to the cast thereon.

4. In the process of making stereotypes, the method of preparing the matrix which consists in coating the face thereof with, zinc stearate, intermixed with a relatively small proportion of powdered graphite, thereby to ll in the interstices o said face in the roasting of the matrix, and rendering the said face smooth, unbroken and non-adherent to the cast thereon.

5. In the process of making stereotypes, the method of preparin the matrix which consists in coating the ace thereof with, a composition consisting of comminuted zinc stearate and graphite in approximately the proportions stated and intermixed with each other in the presence of naphthalene crystals substantially as described whereby to fill the interstices of and rendering' the face of the said matrix smooth, lunbroken and nonadherent to the cast thereon.

ALBERT W. COCHRAN. HENRY W. DEWEY. 

